1. Field of the Invention
This invention relates to a self-aligning roller bearing in which the occurrence of edge stress in the surfaces of contact between rollers and races is eliminated or decreased.
2. Related Background Art
In the prior-art self-aligning roller bearing, the state of contact between an inner race or an outer race and a roller is the contact between single arcs when viewed in a plane containing the generator of the roller, and this leads to the following disadvantages:
(1) When the rate of contact between the arc of the generator of the roller and the arc of the generator of the race is increased, the edge stress in the portion of contact sharply increases as the load increases, and there arise problems such as a short life, abrasion, plastic deformation and seizure.
(2) If said rate of contact is decreased to avoid the occurrence of such edge stress, the load range in which a state of point contact is provided increases, and there arise problems such as a short life, reduced rigidity, abrasion and plastic deformation.
To overcome these disadvantages, Japanese Patent Application Laid-Open No. 60-175818 discloses a self-aligning roller bearing in which the generator of the track surface is constituted by a curve having a plurality of radii of curvature, and in this bearing, the rate of contact between the races and the rollers is decreased from the center of contact toward the edge portion to thereby achieve the prevention or reduction of the edge stress.
However, the self-aligning roller bearing disclosed in the aforementioned Japanese Patent Application Laid-Open No. 60-175818 suffers from the following problems:
(1) The position of contact between the outer race and the roller is not fixed due to the self-aligning action of this, but is variable in the axial direction. Therefore, even if a curve having a plurality of radii of curvature is given to the track surface of the outer race, the optimum performance of the bearing cannot be effectively obtained.
(2) Since at least the generator of the track surface of the inner race is a curve having a plurality of radii of curvature, the bearing displays its optimum performance only in the design operating condition of the inner race. Consequently, in order that the bearing may be used in different operating conditions, bearings having inner races differing in the shape of the generator must be severally prepared.
Where a plurality of operating conditions are contemplated, it is more advantageous in manufacture to adjust the curvature of the rollers to several kinds of groups and to combine them with the inner and outer race track surfaces in accordance with the operating conditions rather than to manufacture inner and outer races having their curvatures adjusted intricately in accordance with the operating conditions.